The present invention relates to a catheter such as an epidural catheter, and more particularly to such a catheter characterized by a limited longitudinal extension and increased pull strength.
In its basic form, a catheter is essentially a flexible tube formed of plastic defining a tube proximal end, a tube distal end, and a tube body connecting the tube proximal and distal ends such that liquid entering one tube end passes through the tube body and exits through the other tube end. Improved catheters frequently have a helical spring coil formed of metal defining a coil proximal end, a coil distal end, and a coil connecting the coil proximal and distal ends. The coil is coaxially disposed within the tube for the purpose of limiting, and hopefully precluding, kinking of the tube during its insertion into and passage through a patient's body. The tube and coil are separately formed, but are typically substantially coextensive longitudinally. During assembly the tube is expanded radially in inner diameter (for example, through the use of a solvent), the coil is then inserted into the tube, and the tube is then allowed to return to its original dimensions (for example, through solvent evaporation) such that it snugly hugs the coil.
A particularly useful embodiment of such a catheter (especially for an epidural catheter) uses a coil which is axially or longitudinally expanded at or adjacent the coil distal end so that the tip or distal end of the catheter is softer and more flexible than the proximal remainder of the catheter. The soft, flexible tip of such a catheter embodiment enables it to more closely and safely follow an intended tortuous path through the body passageways (e.g., veins).
When it comes time for the removal of a catheter from the patient, the pull force exerted on the catheter by the medical personnel typically results in an elongation or longitudinal extension of the catheter (both within and without the patient's body) as neither the plastic tube nor the metal coil exhibits any high resistance to elongation (that is, any high pull strength). For example, a nineteen gauge catheter with a length of 35½ inches may exhibit an elongation of about 15 inches in response to a pull force of 8 pounds. Such a high elongation and low pull strength is undesirable since it increases both the energy and time required for medical personnel (e.g., a surgeon) to remove the catheter from the patient.
Accordingly, it is an object of the present invention to provide a catheter which exhibits a limited longitudinal extension and high pull strength.
Another object is to provide such a catheter which in one preferred embodiment can be more easily and rapidly removed from a patient than a conventional catheter.
A further object is to provide such a catheter which in one preferred embodiment is a nineteen gauge catheter which exhibits an elongation of less than 4 inches at a force of 11 pounds.
It is also an object of the present invention to provide such a catheter which is simple and economical to manufacture, use, and maintain.